// 一次初始化 pthread_once_t
 
/*
用到的API：
pthread_once_t once_control = PTHREAD_ONCE_INIT;
int pthread_once(pthread_once_t* once_control, void (*init_routine)(void));
    
    有些事需要一次且仅需要一次执行。通常当初始化应用程序时，可以比较容易地将其放在main函数中。
	
	但当你写一个库时，就不能在main里面初始化了，你可以用静态初始化，但使用一次初始化（pthread_once_t）
	
	会比较容易些。
 */


// 例程：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h> 
//#include <errors.h>
 
 
pthread_once_t once_block = PTHREAD_ONCE_INIT; 
pthread_mutex_t mutex; 
 
 
/*This is the one-time initialization routine. It will be 
* called exactly once, no matter how many calls to pthread_once 
* with the same control structure are made during the course of 
* the program. 
*/ 
 
void once_init_routine (void) 
{
    int status; 

    status = pthread_mutex_init (&mutex, NULL); 

    if (status != 0) 
        exit(-1); 
}
 
/* 
 Thread start routine that calls pthread_once. 
 */
void *thread_routine (void *arg) 
{
    int status; 
    status = pthread_once (&once_block, once_init_routine); 
    if (status != 0) 
        exit(-1); 
    status = pthread_mutex_lock (&mutex); 
    if (status != 0) 
        exit(-1);
    printf ("thread routine has locked the mutex.\n"); 
 
    status = pthread_mutex_unlock (&mutex); 
    if (status != 0) 
        exit(-1); 
    return NULL; 
}
 
int main (int argc, char *argv[]) 
{
    pthread_t thread_id; 
    char *input, buffer[64]; 
    int status; 

    status = pthread_create (&thread_id, NULL, thread_routine, NULL); 
    if (status != 0) 
        exit(-1);

    status = pthread_once (&once_block, once_init_routine); 
    if (status != 0) 
        exit(-1);

    status = pthread_mutex_lock (&mutex); 
    if (status != 0) 
        exit(-1); 
    printf ("Main has locked the mutex.\n"); 

    status = pthread_mutex_unlock (&mutex); 
    if (status != 0) 
        exit(-1);

    status = pthread_join (thread_id, NULL); 
    if (status != 0) 
        exit(-1);
    return 0; 
}
